Assessing the Effects of Nitrogen Deposition on Alpine Plant and Soil Communities.

Nitrogen deposition is increasing in the Western United States; increased
availability of nitrogen due to anthropogenic N deposition has been linked to
eutrophication, changes in plant and microbial diversity, and soil acidification.
High-elevation nutrient-limited ecosystems are considered particularly vulnerable to
N deposition. Here we present results from a 3-year fertilization study of three
alpine ecosystems - at Mount Rainier, North Cascades, and Olympic National Parks - in
the Pacific Northwest. We used 15N-labeled ammonium nitrate to simulate three levels
of nitrogen. Preliminary data show increases in both short- and long-term
availability of inorganic nitrogen in soil solution, as well as increases in ambient
nitrogen deposition. We will present changes in soil nutrient availability, plant
diversity and growth, soil microbial community, and soil nitrogen-mineralizing
capacity and their implications for nitrogen critical loads for alpine ecosystems in
the Pacific Northwest.